Often in making decisions about changing behaviors or taking certain medications we weigh health risks or benefits against quality of life considerations. For example, few doctors would recommend that a 90 year-old with a fondness for cheese cake and martinis abstain from those pleasures even if indulging might shorten his or her life a bit. Similarly, many women have made the choice, in consultation with their doctors, to continue estrogen replacement therapy long term despite the small but now well-established risks such therapy entails, simply because estrogen makes them feel so much better.
A great example of how the desire to live better is sometimes at odds with the desire to live longer is the diet called "CR" (calorie restriction). The diet, which is said to extend life and prevent diseases associated with aging, consists of eating a very low-calorie but nutritionally balanced diet that meets 100% of vitamin, mineral, protein, and essential fat needs. For most people, though, such a restricted diet might seem incompatible with normal and enjoyable life.
According to a column on InteliHealth.com by Julie Redfern, a senior nutritionist at Brigham and Women's Hospital, CR gained momentum in the 1930s after studies on mice showed that reducing their normal food intake by about 40% increased their maximum life span by 30% to 40%. Since then, research on worms and monkeys has shown that CR works in other species. In humans, CR has recently been shown to improve (decrease) markers of cardiovascular aging such as core body temperature and fasting insulin levels in obese people. Whether similar calorie restriction would also benefit people who have normal body weight has not been proven.
The mechanisms behind CR are still theoretical. CR may redirect energy away from growth and reproduction toward cell maintenance, repair, and protection. Another theory is that CR may shift the body into preservation mode where damage is more efficiently corrected. Based on this theory, CR is not recommended for those younger than 18 or for pregnant women.
Severe calorie restriction as a means of prolonging life has several practical and theoretical problems. First, a diet of 1000 â€“ 1200 calories per day would be intolerable to most Americans who have trouble limiting intake to even twice that amount. Second, the success of CR in prolonging animals' lives may be misleading because of different energy needs among species. Mice, for example, expend exponentially more energy on reproducing and nursing than humans. Third, human maximum lifespan may have little room to expand compared to that of animals. The maximum human lifespan recorded so far is of a 122-year old French woman. Finally, CR can be unhealthful: weight can drop to dangerously low levels where menstruation ceases in women. CR may also increase the risk of osteoporosis, especially if the diet is too low in calcium and vitamin D. Cold intolerance, weakness, decreased sex drive, food obsessions, hording, obsession with conserving energy, and seeking vicarious food experiences through TV or cooking for others are other possible effects.
The Calorie Restriction Society, an organization whose website offers support, data, and menu tips for people wishing to pursue CR, has the motto "Fewer Calories. More Life." There's no doubt that overindulging in food can decrease both the quality and the length of your life if it leads to diabetes and other illnesses. But one wonders, even if the animal data on severe calorie restriction's effect on longevity is further confirmed in humans, whether "more life" is always better life. Then again, at 1000 calories a day, maybe life just seems longer.
Can you imagine going on a CR-like diet? If you follow one or have in the past, tell us about the experience.
Dr. Suzanne Koven practices internal medicine with a special interest in weight issues at Massachusetts General Hospital in Boston, and teaches at Harvard Medical School.
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